What is toner? 

"The idea is to thoroughly cleanse and clarify via your double cleanse, then use a toner as the first leave-on step that hydrates and treats."

To put it simply, toner looks like water and acts like water. A toner is a fast-penetrating liquid that delivers skin a quick hit of hydration and helps remove some dead cells off the surface of the skin. The result: plump, glowy skin, toner is like a primer for the rest of your skin-care routine like serums and moisturizer, - Allure